The present invention relates generally to valve deactivating devices for internal combustion engines and, in particular, to an apparatus for controlling the operation of a valve in an internal combustion engine.
Internal combustion engines are well known. Internal combustion engines include a valvetrain having intake and exhaust valves disposed in the cylinder head above each combustion cylinder. The intake and exhaust valves connect intake and exhaust ports with each combustion cylinder. The intake and exhaust valves are generally poppet-type valves having a generally mushroom-shaped head and an elongated cylindrical stem extending from the valve head. A spring biases the valve head in a fully closed position against a valve seat in the cylinder head. Historically, engine valves were actuated from the fully closed position to a fully open position by an underhead camshaft, pushrod, and rocker arm assembly. Hydraulic lifters, which utilize pressurized hydraulic fluid to actuate a piston to reciprocate the valve, were added as a buffer between the motion of the rocker arm and the valve stem and as a means for adjusting valve lash. In later developments, overhead camshafts eliminated the pushrod and, occasionally, the rocker arm for a more direct actuation of the valves.
Devices for deactivating engine valves, known in the art as lost motion devices, are also well known. Lost motion devices are advantageous because they increase the efficiency of the engine by either completely eliminating or reducing the stroke of the valve, thereby allowing no or reduced fuel-air mixture or engine exhaust, respectively, to enter or exit the cylinder respectively. Prior art lost motion devices have utilized different means to deactivate the valve including varying the output of the hydraulic fluid pump and reducing the force of the lifter. Other prior art lost motion devices utilized solenoid valves to control when lifters were active or inactive. Regardless of the means for deactivating the engine valve, most modern lost motion devices are activated by a control means that determines when the means for deactivating the valve is to be engaged or disengaged.
Prior art hydraulic lost motion devices, however, do have disadvantages. Many prior art lost motion devices have only two positions, either engaged, whereby the valve completes a full stroke, or disengaged, whereby the valve does not complete a stroke at all, rendering that particular cylinder inactive for that engine cycle. In addition, prior art lost motion devices have losses associated with the hydraulic system and require a separate accumulator to recover the hydraulic energy. Another limitation of prior art lost motion devices has been their inability to produce the equivalent of cam ramp motion, accelerating and decelerating the valves slowly enough to prevent valve bounce, wear, noise, and high Hertz stresses.
The art continues to seek improvements. It is desirable to provide an apparatus for controlling the operation of a valve in the internal combustion engine that does not have losses associated with prior art hydraulic systems. It is also desirable to provide an apparatus for controlling the operation of a valve in the internal combustion engine that can prevent valve bounce, wear, noise and high Hertz stresses, and that has more than two positions.
The present invention concerns an apparatus for controlling the operation of a valve in an internal combustion engine. The apparatus includes a lost motion sleeve having a stepped generally tubular body with a larger diameter portion terminating in a first open end and a smaller diameter portion terminating in a second open end opposite the first end. The second end is adapted to slidingly receive a stem piston in contact with a stem end of an engine valve. The apparatus also includes a generally cylindrical rocker piston having a lower end and an upper end. The lower end of the rocker piston is slidingly disposed in the first end of the sleeve. The apparatus also includes a clamping means being selectively activated for retaining the sleeve. The clamping means is preferably an electrically actuated piezoelectric or magnetostrictive clamping block. A generally non-compressible fluid, such as engine oil, is introduced in the larger diameter portion of the sleeve. Alternatively, the lower end of the lost motion sleeve receives a lash adjustment piston in addition to the rocker piston for providing lash adjustment for the engine valve actuation. By placing a lash adjustment piston in the lost motion sleeve, the lash adjustment function can be advantageously removed from the rocker arm pivot, simplifying the rocker arm pivot, as compared to the prior art.
When a stem piston contacting a stem end of an engine valve is inserted into the second end of the lost motion sleeve and the clamping means is activated to retain the sleeve, force applied to the upper end of said rocker piston will move the rocker piston toward the second end of the lost motion sleeve and act upon the valve stem through the fluid causing the valve to move. When the clamping means is not activated, the force will act upon the lost motion sleeve through the hydraulic fluid, causing the lost motion sleeve to move relative to the valve stem and prevent a portion of the force acting upon the valve stem from exceeding a predetermined amount required to move the valve.
Alternatively, because electrically actuated piezoelectric or magnetostrictive clamping blocks generally produce a very short stroke, the apparatus includes a multiplier assembly for multiplying the stroke of the clamping block in order to produce a useful clamping device. The multiplier assembly includes a large piston that is moved by the clamping block, which will drive a volume of hydraulic fluid. The volume of hydraulic fluid moves a smaller piston a distance that is longer by the amount of the piston area ratio and provides a clamping force to the lost motion sleeve.
Unlike prior art cylinder deactivation devices, such as those using locking pins in lifter devices, the present invention can be advantageously locked in a multitude of positions. The friction clamping allows the lost motion sleeve to be stopped in any position in its allowed stroke, and at any time during its motion. This allows the engine controller to select which portion of the cam motion will be transmitted from the cam lobe to the valve.
In operation, if the cam motion is initiated with the lost motion sleeve locked, the valve will begin to move with the initial ramp, following the cam. If at any time the controller unlocks the lost motion sleeve, any further motion of the cam will be absorbed by the motion of the lost motion sleeve against its spring, and the valve spring will drive the valve closed, also displacing oil by motion of the lost motion sleeve. In this way the engine valve motion will have controlled reduction of lift and shortening of duration, with opening timing left in its original location.
Similarly, if the cam motion is started with the lost motion sleeve unlocked, the initial motion of the cam will displace oil that moves the sleeve, leaving the engine valve stationary. If at any time on the opening ramp or flank of the cam the engine controller locks the lost motion sleeve with the clamp, the engine valve will begin to move at that time, traveling the remaining stroke left from that point on the cam. This strategy produces a valve motion with a later opening time, an earlier closing time, shorter duration, and reduced valve lift from the conventional full motion of the cam. This version of the valve motion would have its center point at the same timing as that ground on the camshaft.
The engine design strategy using the present invention would be to design a camshaft with the largest desired valve lift and duration required at any operating point, and would be reduced as dictated by the engine controller to be optimum at all other operating points. The timing could be altered to some extent by the present invention, and complete control of timing could be accomplished by the addition of a conventional cam phasing device.
The present invention has several advantages over the prior art in lost motion hydraulic systems. The most important of these advantages is the reduced losses associated with the hydraulics of the system. Since the hydraulic fluid is displaced without passing through passages and solenoid valves, the losses associated with these parts are largely eliminated. Prior art lost motion devices also required a separate accumulator to recover the hydraulic energy, and in the present invention the lost motion device and the accumulator are one component, reducing cost and complexity.
Another limitation of prior art lost motion devices has been their inability to produce the equivalent of cam ramp motion, accelerating and decelerating the valves slowly enough to prevent valve bounce, wear, noise, and high Hertz stresses. In the present invention, since the force generated by the clamping block can be varied by altering the applied signal, and since the clamping block is a friction device, the actuation of the lost motion sleeve and, consequently, the motion transmitted to the valve, can be done gradually by the relatively slow application of the frictional clamping force. This provides a clutch effect to reduce acceleration to acceptable levels.
The present invention allows engine valves to be rapidly and selectively disabled or allows engine valves to operate normally. A number of advantageous fuel economy, emissions, and fuel efficiency strategies can be accomplished by this selection of valve operation.